A Little Explosive History

Sunday

Jan 29, 2017 at 12:01 AMJan 31, 2017 at 3:47 PM

Dawny G

An extinct volcano has not erupted in 10,000 years and probably will never do so again. The shifts in the earth's plates have likely eliminated its lava supply and moved the geologic hot spots away from the volcano. New Hampshire's Ossipee Mountain (near the White Mountains) is an extinct volcano.We are going to hike active volcanoes: Mount Hood, Mount Adams, and Mount Saint Helens. An active volcano has the potential to erupt. If it's not doing anything, it's dormant (like a sleeping giant). But the sleeping giant can wake up.....Mount Hood, about 11,200 feet high, is more than 500,000 years old. Records indicate that there have been periods of frequent eruptions followed by quiet interludes of hundreds of years. The last eruption was 1907.Mount Adams is about 520,000 years old. I've found drastically different records of its most recent eruption, ranging from 500 BCE to about 950 CE. I feel fairly safe either way.And then there's Mount Saint Helens. About 8,360 feet high (used to be higher) and 40,000 years old (a baby), Mt. St. Helens is not only active, it's been active a lot. The most recent eruption was 2008. There was a series of eruptions between 2004 and 2008. But the best known is the 1980 eruption.

Mt. St. Helens 1980 eruption, from history.comIn 1980, Mt. St. Helens blew off 1,300 feet (1/4 mile) of its peak, left a one mile crater, created a massive landslide of debris that traveled almost a mile and raised the air temperature in the vicinity to over 800 °F. Fifty-seven people were killed, nearly 300 homes and almost 200 miles of highway were destroyed. Old growth forest was blown away, and ash and debris choked the mountain streams. Sound daunting? I urge you to view this video, less than three minutes long, https://www.youtube.com/watch?v=IhU6jml6NY4 to see the eruption. (If you're interested, a second video of about seven minutes will follow.)

In December, 1989, there were a few 'smaller' eruptions that began to rebuild the mountain's peak. The most recent eruption was 2008.

When Mt. St. Helens began to rumble in 1980, seismologists installed stations that monitor all the activity, assuring that there will be no surprises. The area remains active, with millions of signals recorded (some obviously detectable only by special equipment).

¨My adventures in the Cascades took place when Mt. St. Helens was fairly quiet, between some small 'dome building' activity in December, 1989 the 2008 eruption. And it was still just amazing. # # #